Homopolar bearingless slice motors
Described are homopolar bearingless slice motors which include an array arrangement of permanent magnets on stator teeth, and a magnet-free rotor having a unique surface geometry. Also described are related components of such motors. The permanent magnet arrays provide homopolar bias flux to the rotor, and salient features on the rotor surface route the bias flux toward paths desirable for force and torque generation. In an illustrative embodiment, two magnet arrays are placed at the tips of stator teeth, so as to provide the bias flux via relatively short flux paths. By modulating current through windings based upon the rotor radial and angular position measurements, the stator can levitate and rotate the rotor.
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This application claims the benefit of U.S. Provisional Application No. 62/718,478 filed on Aug. 14, 2018 and entitled “HOMOPOLAR BEARINGLESS SLICE MOTORS,” and claims the benefit of U.S. Provisional Application No. 62/609,711 filed Dec. 22, 2017 and entitled “HOMOPOLAR BEARINGLESS SLICE MOTORS,” which applications are hereby incorporated herein by reference in their entireties.
GOVERNMENT RIGHTSThis invention was made with Government support under Grant No. R41 HL134455 awarded by the National Institutes of Health. The Government has certain rights in the invention.
BACKGROUNDAs is known in the art, a homopolar motor is an electric machine in which magnetic poles of a rotor as presented to a stator are provided have the same polarity along the rotor circumference, e.g., north-north-north-north. This characteristic makes homopolar motors different from conventional motors which typically have rotors with alternating magnetic poles along the rotor circumference, e.g., north-south-north-south.
As is also known, a bearingless motor is an electric machine having a rotor suspended at a center of a stator bore via magnetic levitation. The stator generates forces to magnetically levitate the rotor and also provides a torque to rotate the rotor. Such motors are suitable for applications that benefit from contact-free operations, such as blood pumps.
As is further known, a slice motor is a particular type of bearingless motor in which a rotor is provided having an aspect ratio (defined as rotor axial height divided by rotor diameter), designed to be sufficiently small to make some rotor degrees of freedom passively stable. Such a design reduces the number of rotor degrees of freedom requiring active stabilization via feedback controls, thereby saving components such as sensors, windings, and power amplifiers.
A homopolar bearingless slice motor is thus an electric machine that transforms input electric power to output mechanical power in a rotational form (i.e., a product of a torque and rotational speed) with a rotor having a desired aspect ratio. Such motors can be utilized in any applications that need rotary actuators and drives. Also, such motors utilize magnetic levitation. Thus, homopolar bearingless slice motors are particularly suitable for applications which benefit from contact-free rotary actuation.
Such motors can be utilized, for example, in bearingless centrifugal pumps that drive liquids sensitive to mechanical stress and heat, e.g., bloods and biological samples. Also, since the magnetic levitation can reduce, or in some cases eliminate, the usage of lubricants and generation of debris, such motors can be utilized for bearingless centrifugal pumps that drive liquids requiring a high level of purity control, e.g. such as in the semiconductor industry and chemical process industries.
Bearingless slice motors having temple-shaped stator armatures which drive permanent-magnet rotors have been developed as have bearingless motors that drive permanent-magnet rotors, and bearingless pumps using such motors. Also known are homopolar bearingless slice motors having a so-called “temple” design, where both of the stator and the rotor have magnets for homopolar flux-biasing.
Some slice bearingless motors have also been developed that allow decoupled rotation suspension control. Bearingless motors utilizing a permanent magnet-free structure for disposable centrifugal blood pumps are also known.
SUMMARYDescribed herein are concepts and structures for homopolar bearingless slice motors.
In accordance with one aspect of the concepts, systems and techniques described herein, permanent magnets disposed on end portions of stator teeth closest to a surface of a rotor in a homopolar bearingless slice motor provide homopolar bias flux to a rotor.
With this arrangement, a homopolar bearingless slice motor having a flux path which is shorter that a flux path provided in conventional homopolar bearingless slice motors is provided. Providing a shorter flux path enables reduced usage of permanent magnets.
In embodiments, the permanent magnets may be provided from a pair of permanent magnet arrays which provide homopolar bias flux to the rotor. In an illustrative embodiment, two magnet arrays are placed at ends (or tips) of the stator teeth, so as to provide a bias flux via relatively short flux paths between the stator teeth and the rotor. By modulating a current through a winding based upon rotor radial and angular position measurements, the stator can levitate and rotate the rotor.
In embodiments, a first one of the magnet arrays is disposed on a first surface of ends of the stator teeth and a second array of magnets is disposed on a second opposing surface of ends of the stator teeth.
In embodiments, the magnet arrays are provided in a Halbach configuration.
In accordance with a further aspect of the concepts, systems and techniques described herein, a magnet-free rotor of a homopolar bearingless slice motors is provided having a surface from which project structures (also referred to as “salient features” or “members”) having a geometry selected to route a bias flux provided by permanent magnets disposed thereabout toward paths desirable for force and torque generation.
With this particular arrangement, one or more permanent magnets or permanent magnets arrays may provide a homopolar bias flux to the rotor, and the salient features on the rotor surface route the bias flux toward paths desirable for force and torque generation. In an illustrative embodiment, two magnet arrays are placed at the tips of stator teeth, so as to provide the bias flux via relatively short flux paths. By modulating the current through the winding based on the rotor radial and angular position measurements, the stator can levitate and rotate the rotor. In embodiments, the permanent magnets are disposed on ends of a stator proximate a surface of the rotor.
Compared to prior art motors, the motor designs described herein differ in at least several respects. First, the homopolar bearingless slice motor described herein utilize flux-biasing permanent magnets. In one embodiment, the flux-biasing permanent magnets are arranged in a Halbach-type array configuration disposed around an outer surface of a rotor. Second, the homopolar bearingless slice motor described herein utilizes rotors having salient features that are coupled to a homopolar bias-flux.
In embodiments such salient features include, but are not limited to radial fins projecting from one or more surfaces (e.g. top and/or bottom surface of the rotor). In embodiments, such salient features include radial fins projecting from one or more surfaces (e.g. top and/or bottom surface of the rotor) and one or more structures (or members) provided on a side surface of the rotor. In embodiments, such salient features include radial fins projecting from one or more surfaces (e.g. top and/or bottom surface of the rotor) and a magnetic material disposed around a side surface of the rotor. Third, the homopolar bearingless slice motor described herein utilizes a stator having a winding scheme that physically separates windings for rotation functions from windings for bearing functions (i.e. the motor design described herein utilizes two separated windings: rotation windings and suspension windings). This approach reduces the number of power amplifiers required to drive the motor. Fourth homopolar bearingless slice motors provided in accordance with the concepts described herein utilize rotors which do not contain permanent magnets. Rather, homopolar bearingless slice motors provided in accordance with the concepts described herein utilize permanent magnets disposed in a Halbach array configuration and arranged on a stator and around a perimeter of a surface of the rotor outer. Furthermore, homopolar bias-flux enables decoupled rotation-levitation control.
The motor design described herein differs from prior art slice bearingless motors that allow decoupled rotation suspension control in several aspects. First, as noted above, the motor design described herein utilizes rotors which do not contain permanent magnets. Second, the motor design described herein utilizes coils forming the suspension winding which are all concentric. That is, each coil is only engaged with a single stator tooth. This approach differs from suspension winding designs in prior art slice bearingless motors in which where some coils forming a suspension winding span more than one stator tooth.
The motor design described herein differs from prior art bearingless motors utilizing a permanent magnet-free structure for disposable centrifugal blood pumps in the sense that the stator of the motor described herein has Halbach magnet arrays that provide homopolar bias-flux to the rotor. This approach enables at least two motor features: (1) decoupled rotation-suspension control; (2) less copper loss for suspension; and (3) Improved passive stiffness on the axial translation and out-of-plane tilts.
Accordingly, described herein are new flux-biasing designs. In embodiments, the flux-biasing is provided from permanent magnets disposed in a Halbach array configuration and disposed on a portion of stator teeth proximate an outer surface of a rotor. This approach results in a homopolar bearingless slice motors having characteristics which are favorable compared with like characteristics of existing homopolar bearingless slice motors. First, the techniques and structures described herein result in a single-sided air gap, i.e., the rotor is magnetically engaged with the stator only via a single (so-called “outer”) air gaps. This allows the rotor inside to be used for other purposes, such as placing an embedded impeller or position sensors. Second, shorter flux path enables reduced usage of permanent magnets.
Elimination of permanent magnets from the rotor allows several benefits over the existing permanent-magnet bearingless motors. First, the rotor cost can be reduced by saving material and manufacturing costs. This can particularly advantageous to bearingless motors that require frequent rotor replacement, for example extra-corporeal blood pumps where the impeller-rotor unit should be disposed for each patient each time. Second, magnet-free rotors are more robustness to high-speed and high-temperature operating conditions.
Since no mechanical connections, such as bearings and shafts, are involved for the rotor suspension and torque generation, the motor described herein can be used for pumping delicate fluids such as biological samples. For example, the pump can be used as a blood pump to reduce the level of hemolysis and thrombosis. Also, the magnetic levitation eliminates unnecessary chemicals such as lubricants, which is beneficial for chemical processes that require a tight purity control. Potential commercial applications of this technology includes but is not limited to: miniature pumps for delivering delicate bio-medical samples that only allow a limited amount of exposure to mechanical stress and heat; and precision pumps for chemical processes and semi-conductor industries that requires a tight level of purity control.
Although the concepts described herein find application for use with the fluid pumps, the concepts are not limited to use with fluid pumps. Indeed, the broad concepts described herein can be applied to any areas or application that benefits from contact-free rotary actuation, including, but not limited to: high-speed spindles for machining; bearingless turbines; bearingless generators; electric vehicles; and turbochargers.
The foregoing and other objects, features and advantages will be apparent from the following more particular description of the embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the embodiments.
Referring now to
Homopolar bearingless slice motor 10 further includes a magnet-free rotor 18 having a unique surface geometry. Illustrative surface geometries of rotor 18 will be described in detail below. Suffice it here to say that rotor 18 is provided having an outer surface 18a which routes a bias flux provided by permanent magnets 14 toward paths desirable for force and torque generation. In this illustrative embodiment, rotor surface 18a is provided having salient features 20 which route a bias flux provided by permanent magnets 14 toward paths desirable for force and torque generation. In other embodiments, the magnet-free rotor 18 can have a substantially smooth surface and have internal channels or grooves that are configured to route the bias flux.
In embodiments, the permanent magnet arrays 16a, 16b provide homopolar bias flux to the rotor 18, and the salient features on the rotor surface route the bias flux toward paths desirable for force and torque generation.
In the illustrative embodiment of
In embodiments, salient rotor features include, but are not limited to, fins 5a-b projecting from one or more surfaces (e.g. top and/or bottom surfaces of the rotor). In an embodiment such salient features include radial fins projecting from one or more surfaces (e.g. top and/or bottom surface of the rotor) and one or more members 20 (or rotor “teeth”) provided on a side surface of rotor 18. In an embodiment, such salient features include radial fins projecting from one or more surfaces (e.g. top and/or bottom surface of the rotor) and a magnetic material disposed around a side surface of the rotor. The rotor teeth 20 can be made of a low-carbon steel and be magnet-free. In an example embodiment, the rotor 18 is made of a single low-carbon steel piece with its peripheral surface machined to comprise radial fins 5a-b and rotor teeth 20. In another embodiment, a rotor (e.g., the rotor 18b of
Referring now to
A ring-shaped rotor 18 may then be inserted or otherwise disposed into the stator bore. In embodiments, ring-shaped rotor 18 may be formed or otherwise provided from low-carbon steel, e.g., AISI 1018. In other embodiments, the rotor 18 can comprise a material that exhibits high magnetic permeability. For example, the rotor 18 can comprise any ferromagnetic materials exhibiting relatively low hysteresis (called magnetically soft materials). The outer surface of the rotor has salient features 20 having mechanical and/or magnetic properties selected such that salient features route homopolar bias-flux from magnet arrays 16a, 16b (
End (or tips) 17 of the stator teeth 12 directed toward (or facing) rotor 16 are coupled via two magnet arrays 16a, 16b. One magnet array, here array 16a, is aligned with the rotor top surface 41a, and the other magnet array, here array 16b, is aligned with the rotor bottom surface 41b. The design details of the magnet arrays and its possible design variations are described in more detail further below.
In the illustrative embodiment of
As most easily viewed in
The measured rotor radial positions and rotational angle are used for feedback control of the bearingless motor. The bearingless motor is a closed-loop system comprising sensors, a controller, power amplifiers, and motor hardware. The details and possible variations of control systems are described in more detail further below.
Referring now to
As in other typical motors, the stator armature of the illustrative motor can be made of electrical steel, for example with 0.33 mm lamination thickness. Thinner lamination is better if the motor excitation frequency is relatively high, but thicker lamination or even a solid steel can be used if the excitation frequency is relatively low, and therefore iron loss is not a significant concern. When an AC magnetic flux passes through a permeable and conductive material (such as iron), the flux is not uniformly distributed across the cross section—it is rather localized in the vicinity of the outer surface called “skin depth”. This is because the AC magnetic flux induces eddy currents inside the material and this buck out the magnetic flux. This means that the material is underutilized. Also, the induced eddy currents dissipate heat, and increase “iron (power) loss”. Accordingly, embodiments of the invention laminate the material, so that the thickness of the lamination is similar to the skin depth, to fully utilize the magnetic material to conduct magnetic flux, and also minimize the power loss.
In the illustrative embodiment shown in
Referring now to
As shown also in
The stator bottom 24 has circularly disposed rectangular (or generally rectangular) holes 51a-N into which ends of the stator teeth can be inserted. In general openings 51 are provided having a shape selected to accept the cross-sectional shape of an end of stator teeth 12 to be disposed in the openings. In embodiments, the dimensions of openings 51 are selected so as to provide a press fit with the ends of teeth 12 so as to secure teeth 12 to stator bottom 24. Other techniques for securing stator teeth 12 to stator bottom plate 24 may also be used including but not limited to fastening techniques, welding techniques, epoxy techniques, and 3D printing techniques.
The stator bottom 24 has one central hole 52, and two sets of circularly disposed holes 54a-N, 55a-N. The central hole 52 can be used to insert a structure that mounts magnet arrays and position sensors. The set of twelve holes 55a-N arranged closer to the stator teeth can be used to pass the winding leads and make the connections under the stator bottom 24. The set of four holes 54a-N arranged closer to the center can be used to fasten the structure mounting sensors and magnet arrays.
The stator armature (e.g., the stator armature 13 of
The temple-shaped armature is topologically equivalent to typical planar stator structure. That is, by flattening the L-shaped teeth, one can provide a planar stator structure that can implement the same magnetic design. Also, the stator can have more than twelve stator teeth.
Referring now to
The rotor 18c shown in
The reluctance rotor 18c is ring-shaped, and its thickness/outside-diameter ratio (T/OD) is relatively small. Table 1 lists nominal values of geometric parameters of an illustrative reluctance rotor. The inner cylindrical surface 19a of the rotor can be used for eddy-current sensors to measure the rotor radial positions, as shown in
The outer surface 19b of the reluctance rotor 18c has unique salient features including 20a and 5a-b. The rotor has two circular fins 5a-b protruding radially outwards, one from the top 5b and the other from the bottom 5a. These fins 5a-b are where the homopolar bias flux from the magnet arrays enter (or leave if the magnetization of the magnet arrays is reversed) the rotor 18c. Having small fin thickness t, e.g., t<1 mm, can help magnetic levitation. This is because the bias flux can saturate the thin fins 5a-b more easily, and the magnetic saturation makes the variation of the magnetic flux density in the fins 5a-b relatively insensitive to the rotor position variation, thereby leading to smaller radial negative stiffness kr.
The axial separation between the fins 5a-b and rotor teeth S should be sufficiently large to achieve good performance in radial force generation. Too small separation S can result in insufficient force/current sensitivity of the levitation system. Also, small separation S can make the radial force not monotonically increasing with respect to the amplitude of the suspension winding MMF, which makes it difficult to lift off an off-centered rotor.
In this illustrative embodiment, between the two fins 5a-b, the reluctance rotor has four teeth equally spaced along the circumference. The rotor tooth (e.g., the tooth 20a of
Referring now to
The number of the rotor teeth can, of course, be fewer or more than four, but more rotor teeth proportionally increases the required electrical frequencies of the rotation winding MMF. That is, given the rotor mechanical speed Ωr, the required electrical frequency for the rotation winding MMF is ωr=pΩr, where p is the number of rotor teeth and equivalently the number of pole pairs of the rotation winding MMF.
Referring again to
The stator has permanent magnets (e.g., magnet array 14 of
Referring now to
In the structure of
As shown in
Referring now to
In the bearingless motor described herein, the homopolar bias-flux makes some rotor degrees of freedom passively stable due to the reluctance force. Specifically, referring to
As noted above, in an illustrative embodiment, the winding of the bearingless motor have 36 coils. In other embodiments, fewer or more coils may, of course, be used. The coil leads are interconnected to form two sets of three-phase windings: suspension winding and rotation winding.
Referring now to
Alternatively, one can implement combined winding scheme, where each stator tooth has a single coil that contributes to both torque and force generations. The combined winding scheme is explained in U.S. patent application Ser. No. 15/227,256 filed Aug. 3, 2016 and assigned to the assignee of the present application and hereby incorporated herein by reference in its entirety.
The suspension winding generates two-pole MMF distribution around the rotor, which induces imbalanced flux density distribution of the homopolar bias-flux and generates radial forces. The principle of radial force generation is similar to that of typical homopolar-biased magnetic bearings.
The suspension winding comprises wye-connected three phases (U,V,W), where each phase comprises eight coils connected in series. The three phases overlap each other on the stator teeth, i.e., each stator tooth 12a-L are engaged with two coils 34a-L, 36a-L from two different phases as shown in
Stator windings comprise rotation winding and suspension windings (e.g., rotation winding 32 and suspension windings 34, 36 of
By applying a balanced three-phase currents, i.e.,
iu=Is cos(θs)
iv=Is cos(θs−2π/3)
iw=Is cos(θs+2π/3);
the suspension winding can generate radial force whose amplitude is controlled with Is and direction is controlled with θs, where θs is the angle of the radial force with respect to the axis x in
Currents through the suspension winding generates two-pole MMF distribution around the rotor. Since the coils in the same phase conducts the same current, the MMF generated by each coil is proportional to the number of turns. Four coils closer to the magnetic axis of the phase, or primary coils, has more number of turns than the others, or secondary coils. There is an optimal turn ratio between the secondary coil N2 and the primary coil N1 to minimize the force coupling between x- and y-axes, which is about N2/N1=0.37. This number is optimal in the sense that the resulting twelve-point MMF sequence has the least total harmonic distortion. For example, the suspension winding can have N1=140 and N2=52.
As explained above at least in conjunction with
Rotation winding generates a rotating eight-pole MMF around the rotor, which interacts with the homopolar bias-flux modulated by the rotor teeth to generate a torque.
The rotation winding comprises wye-connected three phases (A, B, C), where each phase comprises four coils connected in series. The three phases are placed over the stator teeth in a staggered arrangement, as shown in
As explained above at least in conjunction with
The rotation winding 32a-L can generate an eight-pole rotating MMF as excited with a set of balanced three-phase currents:
ia=Ir cos(θr)
ib=Ir cos(θr−2π/3)
ic=Ir cos(θr+2π/3);
Here, Ir is the amplitude of the rotation winding current and θr is the electrical angle of the rotation winding current. The resulting MMF wave has an amplitude NrIr and its mechanical angle of rotation is φr=θr/p with respect to x-axis, where p=4 is the number of pole pairs of the motor MMF. Since ia+ib+ic=0, the negative or positive terminals of three phases can be connected together to form a wye-connected three-phase winding.
Referring now to
Referring now to
The torque generation principle for the reluctance rotors is similar to typical permanent magnet synchronous motors. The torque generation principle for the hysteresis rotors is explained in U.S. patent application Ser. No. 15/227,256 filed Aug. 3, 2016 and assigned to the assignee of the present application.
The bearingless motor described herein forms a closed-loop system with a controller, sensors, and power amplifiers.
Referring now to
The sensors 215 which may be the same as or similar to sensors 21 and 200 described above in conjunction with
The suspension controllers Kx(z) 1540b and Ky(z) 1540c take error signals ex=xref−{circumflex over (x)} and ey=yref−ŷ and generate control efforts ux and uy, respectively. For example, PD controllers or Lead controllers can be implemented for Kx(z) and Ky(z). The control efforts ux and uy are processed via the Inverse Clarke Transformation 1525a to compute three-phase signals uu, uv, and uw as follows:
The signals uu and uv are sent to a three-phase transconductance amplifier 1510a as current commands, and the amplifier drives the suspension winding with currents iu, iv, and iw. Excited with iu, iv, and iw, the suspension winding generates two-pole MMF around the rotor, and therefore a radial suspension force.
The rotation control KΩ(z) 1540a takes an error signal eΩ=Ωref−{circumflex over (Ω)} and computes the q-axis control effort uq. For example, a PI controller can be implemented for Kr(z). The d-axis control effort ud can be set to zero in typical cases, or set to other values if necessary. The two control efforts ud and uq are converted to uα and uβ via the Inverse Park Transformation 1530:
which utilize the estimate of rotor angle {circumflex over (θ)} during the computation. The outputs uα and uβ are sinusoidal signals modulated with ud and uq to transform the quantities in a rotating frame to ones in a stationary frame. Then, the Inverse Clarke Transformation 1525b converts uα and uβ to ua, ub, and uc as follows:
The signals ua and ub are sent to a three-phase transconductance amplifier 1510b as current commands, and the amplifier drives the rotation winding with currents ia, ib, and ic. Excited with ia, ib, and ic, the rotation winding generates.
The rotation controller KΩ(z) 1540a and suspension controllers Kx(z) 1540b and Ky(z) 1540c are decoupled in the sense that KΩ(z) 1540a does not use {circumflex over (x)} and ŷ to compute its control efforts, and Kx(z) 1540b and Ky(z) 1540c do not use {circumflex over (θ)} to compute their control efforts. This characteristic is also explained in U.S. patent application Ser. No. 15/227,256 filed Aug. 3, 2016 and assigned to the assignee of the present application.
The feedback control of the subject bearingless motor requires information on the rotor radial positions, {circumflex over (x)} and ŷ, and rotor rotational angle {circumflex over (θ)}.
One way of obtaining such information is to use sensors (e.g., sensors 21 of
Alternatively, the information on {circumflex over (x)}, ŷ, and {circumflex over (θ)} can be indirectly obtained via estimation algorithms. For example, angle estimate {circumflex over (θ)} can be computed using an observer based on the measurements of the phase voltages and currents.
The bearingless motor design described herein can be utilized to develop bearingless pumps, as shown in
Referring now to
Referring now to
All publications and references cited herein are expressly incorporated herein by reference in their entirety.
Claims
1. A homopolar bearingless slice motor comprising:
- a stator comprising a stator armature and a stator winding, the stator armature having a plurality of stator teeth and the stator winding comprising a plurality of coils;
- an array of permanent magnets disposed on the stator teeth; and
- a magnet-free rotor comprising one or more salient features, wherein the one or more salient features comprise: a first radial fin projecting radially outward from a top surface of the magnet-free rotor, and a second radial fin projecting radially outward from a bottom surface of the magnet-free rotor, wherein the first and second radial fins are axisymmetric with respect to a rotational axis of the rotor and are continuous around the circumference of the rotor; and a plurality of rotor teeth distributed along a circumference of the magnet-free rotor and disposed on an outer surface of the magnet-free rotor and between the first and second radial fins of the magnet-free rotor.
2. The homopolar bearingless slice motor of claim 1 wherein the permanent magnet array provides homopolar bias flux to the rotor and the one or more salient features route the bias flux toward one or more desired paths for force and torque generation.
3. The homopolar bearingless slice motor of claim 2 wherein the array of permanent magnets comprises two magnet arrays, and the two magnet arrays are placed at the tips of stator teeth to provide the bias flux via relatively short flux paths.
4. The homopolar bearingless slice motor of claim 3 wherein in response to modulating currents through the stator winding based on rotor radial and angular position measurements, the stator is configured to levitate and rotate the rotor.
5. The homopolar bearingless slice motor of claim 1 wherein the array of permanent magnets is arranged in a Halbach array configuration and disposed around and proximate to the outer surface of the magnet-free rotor.
6. The homopolar bearingless slice motor of claim 1 wherein the salient features comprise one or more of:
- one or more members provided on a side surface of a rotor;
- and
- a magnetic material disposed around a side surface of the rotor between the radial fins.
7. The homopolar bearingless slice motor of claim 1 wherein the stator has a rotation winding and a suspension winding, where the rotation winding and suspension winding are physically separate windings, thereby reducing a required number of power amplifiers.
8. The homopolar bearingless slice motor of claim 1 wherein a width of each rotor tooth spans a circumferential length of the rotor to cover about two stator teeth.
9. A homopolar bearingless slice motor comprising:
- a magnet-free rotor comprising one or more salient features, the one or more salient features comprising:
- a first radial fin projecting radially outward from a top surface of the magnet-free rotor, and a second radial fin projecting radially outward from a bottom surface of the magnet-free rotor, wherein the first and second radial fins are axisymmetric with respect to a rotational axis of the rotor and are continuous around the circumference of the rotor; and
- a plurality of rotor teeth distributed along a circumference of the magnet-free rotor and disposed on an outer surface of the magnet-free rotor and between the first and second radial fins of the magnet-free rotor.
10. The homopolar bearingless slice motor of claim 9 further comprising:
- a stator comprising a stator armature and a stator winding, the stator armature having a plurality of stator teeth and the stator winding comprising a plurality of coils; and
- an array of permanent magnets disposed on the stator teeth.
11. The homopolar bearingless slice motor of claim 10 wherein the permanent magnet array provides homopolar bias flux to the rotor and the one or more salient features route the bias flux toward one or more desired paths for force and torque generation.
12. The homopolar bearingless slice motor of claim 11 wherein the array of permanent magnets comprises two magnet arrays, and the two magnet arrays are placed at the tips of stator teeth to provide the bias flux via relatively short flux paths.
13. The homopolar bearingless slice motor of claim 12 wherein in response to modulating currents through the stator winding based on rotor position measurements, the stator is configured to levitate and rotate the rotor.
14. The homopolar bearingless slice motor of claim 10 wherein the array of permanent magnets is arranged in a Halbach array configuration and located around an outer surface of the magnet-free rotor.
15. The homopolar bearingless slice motor of claim 10 wherein the salient features comprise one or more of:
- one or more members provided on a side surface of a rotor;
- and
- a magnetic material disposed around a side surface of the rotor between the radial fins.
16. The homopolar bearingless slice motor of claim 10 wherein the stator has a rotation winding and a suspension winding, where the rotation winding and suspension winding are physically separate windings, thereby reducing a required number of power amplifiers.
17. The homopolar bearingless slice motor of claim 9 wherein a width of each rotor tooth spans a circumferential length of the rotor to cover about two stator teeth.
18. A method of operating a homopolar bearingless slice motor, the method comprising:
- rotating a magnet-free rotor comprising one or more salient features within a stator bore defined by a stator armature having a plurality of stator teeth, wherein the one or more salient features comprise:
- a first radial fin projecting radially outward from a top surface of the magnet-free rotor, and a second radial fin projecting radially outward from a bottom surface of the magnet-free rotor, wherein the first and second radial fins are axisymmetric with respect to a rotational axis of the rotor and are continuous around the circumference of the rotor; and
- a plurality of rotor teeth equally distributed along a circumference of the magnet-free rotor and disposed on an outer surface of the magnet-free rotor and between the first and second radial fins of the magnet-free rotor.
19. The homopolar bearingless slice motor of claim 3, wherein a first one of the two magnet arrays is circularly disposed on a top surface of the tips of the stator teeth, and a second one of the two magnet arrays is circularly disposed on a bottom surface of the tips of the stator teeth, wherein the first and the second magnet arrays are symmetric with respect to a midplane of the tips of the stator teeth.
20. The homopolar bearingless slice motor of claim 1 wherein:
- a first set of magnets of the array of permanent magnets is disposed closer to the stator teeth relative to a second set of magnets of the array of permanent magnets;
- the first set of magnets is axially magnetized, and the second set of magnets is radially magnetized; and
- the array of permanent magnets is configured to produce homopolar flux distribution in an air gap between the stator teeth and the rotor teeth.
21. The homopolar bearingless slice motor of claim 12, wherein a first one of the two magnet arrays is circularly disposed on a top surface of the tips of the stator teeth, and a second one of the two magnet arrays is circularly disposed on a bottom surface of the tips of the stator teeth, wherein the first and the second magnet arrays are symmetric with respect to a midplane of the tips of the stator teeth.
22. The homopolar bearingless slice motor of claim 10 wherein:
- a first set of magnets of the array of permanent magnets is disposed closer to the stator teeth relative to a second set of magnets of the array of permanent magnets;
- the first set of magnets is axially magnetized, and the second set of magnets is radially magnetized; and
- the array of permanent magnets is configured to produce homopolar flux distribution in an air gap between the stator teeth and the rotor teeth.
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Type: Grant
Filed: Nov 29, 2018
Date of Patent: Nov 10, 2020
Patent Publication Number: 20190199186
Assignee: Massachusetts Institute of Technology (Cambridge, MA)
Inventors: Minkyun Noh (Cambridge, MA), David L. Trumper (Plaistow, NH)
Primary Examiner: Tran N Nguyen
Application Number: 16/204,042
International Classification: H02K 7/09 (20060101); H02K 21/20 (20060101); H02K 1/24 (20060101); H02K 1/17 (20060101); H02K 11/215 (20160101); H02K 19/10 (20060101); H02K 21/44 (20060101);